Well, unless i'm mistaken, there is still the question of who was controlling the fourth mizukage (though its probably madara since obito didn't really show his face and in that scene it seems Madara had revealed his face). But the Madara then had long black hair and the real Madara at the time had full gray hair.

Another question, during the scene with tobi and sasuke after sasuke's fight with Itachi, why did tobi tried to show sasuke his face? wouldn't sasuke know it's not madara when the real madara's face is all over the village (in some respect, like the final valley)

i don't think that madara is the only guy with long black hair, and we saw that obito's hair had grown long back then, and they are black as well, i guess you are only talking about the fourth mizukage controlling and not the other masked man appearances, and obito fooled everyone that he was madara, and madara's body was connected to mazou to survive, i am pretty sure when the masked man appeared before kisame with the mizukage in control, there wasn't a giant sculpture in that dungeon like temple

for your second question,till the fight between sasuke and itachi, sasuke spent his entire life to gain more power to kill his brother,the only person on his mind was itachi, why would he give a rat's ass about a person long lost in history who had completely no existence in his time, and in that scene after defeating his brother and realizing the truth when he was emotionally vulnerable and psychologically disturbed, why would he question to the identity of the man who told him the truth and that also by comparing him to a person who had become just a history chapter